The invention relates to a method and apparatus for controlling a motor vehicle air conditioning system. A motor vehicle air conditioning system of the known type is described, for example, in EP-PS 0 038 188. Such systems, in addition to the actual control system for the motor vehicle air conditioning system, other separate open-loop or closed-loop control systems exist for individual components in the motor vehicle which can also influence the temperature of the internal space in the vehicle but are completely independent of the actual air conditioning control system. This primarily includes a protection circuit for preventing evaporator icing which causes the compressor to be switched off, a high-pressure or hot gas temperature protection circuit which also acts on the compressor drive or a corresponding clutch, and a cooling water temperature control which causes the radiator fan to be connected or disconnected. Each of these interventions, which take place independently of the actual air conditioning control for the internal vehicle space, influence the capacity of the air conditioning system and thus the air temperature which is supplied to the internal vehicle space via the air conditioning system, thereby also influencing the temperature level in the passenger space.
In addition, refrigeration circuits in vehicles are always subject to alternating boundary conditions such as, for example, drive speed, cooling conditions at the condenser, charging of the evaporator with air and refrigerant, acceleration forces and refrigeration capacity requirement. With separate open-loop or closed-loop control systems, this leads to the compensation of one disturbance variable in one control loop acting as disturbance variables in one or more of the remaining control systems which leads not only to an extremely high switching frequency and extreme burden on the components but also to poor efficiency.